Introduction

Abstract

This introductory chapter begins with a description of the various flow regimes observed in beds of solid particles fluidized with gases or liquids. Distinctions are drawn between the gas-fluidized behaviour of fine, low density particles, Group A in the Geldart classification, larger, more dense materials, Group B, and those more difficult to fluidize at all, Groups C and D. It is shown how gas-fluidized beds behave as the velocity of the gas flowing through them is increased the transitions from bubbling to slugging to turbulent to transport behaviour being described and illustrated by means of schematic diagrams. There then follows a discussion of the historical development of fluidization from its first major industrial application in the 1940s through subsequent decades up to the first decade of the new millennium. Theoretical advances are described from the early “two-phase” theory of Toomey and Johnstone through Davidson's analysis of the flow of gas through bubbling beds to the more recent “particle-bed” model. Industrial applications of gas-fluidized-bed reactors are discussed with reference to fluidized catalytic crackingFluidized catalytic cracking, naphthalene oxidationNaphthalene oxidation, coal to gasoline via the Synthol processSynthol process, propylenePropylene ammoxidation ammoxidationAmmoxidation to acrylonitrileAcrylonitrile, ethylene polymerisation and butane oxidationButane oxidation to maleic anhydrideMaleic anhydride. The wide range of experimental techniques used in basic fluidization research is described as well as the recent application of computational fluid dynamics to gas-solid fluidized systems.